When you face an opponent for the first time, it needn't take you several games to feel out his or her strengths and weaknesses. Use the warm-up period to assess your opponent.
One easy test is to hit a couple of short balls and a couple of deep balls to his or her forehand, then to the backhand. If you detect some uncertainty in one area, file the information away for future reference.
Get an idea also about whether your opponent moves better to the left or the right. That determination also will prove useful during the match.
Once play begins, consider that it might be smarter to save your insight into the other person's weaknesses for critical points, rather than hammer at them obviously and repeatedly.
You'll be well ahead of the game if you have sized up your opponent during the warm-up.